Ground detector circuit



April 29, 1952 T. A. RICH 2,594,994

` GROUND DETECTOR CIRCUIT Filed oct. :51, 195o 2 SHEETS- SHEET 1 Figjl. 5

i Inventor:

Theodore A. Rich,

April 29, 1952 T, A, R|CH 2,594,994

GROUND DETECTOR CIRCUIT Filed OC.. 31, 1950 2 SHEETS-SHEET 2 v Invent-Ghz T h eodore AJQich,

Patented Apr. 29, 1952 UNITED PATENT OFFICE GROUND"DETECTOR CIRCUIT Thodore A. RiliLSchenectady, N. Y., assigner tjoGeral'Elctric' Company, a corporation of NewYork" Application October 31, 1950, Serial No; 193,226V sjolaiin's. (c1. 17a-183) line. Ifa naval vessel is engaged' in a coib'at mission?, it is extremely*4 unfortunate' when a transrnissionv line is' d'eererg'ized toA check` for grounds. All electrically' driven eouiprent `must be Stopped. If both' sides ofv a-Y transmission ,lineI should becerne grounded', there would be a short circuit on the pou/"cr supply; and the resulting high currents :night cause eitenslve daage to Aexlgiensive eiq'uii'n'nentv and to personnel;

Therefore", an importaritobject-of ny' invention is to provide means 1 'dtoti'g`y thempeslce f ground on a d'rtc k' While the trans'llss'di'lv line" `S en Zed'.

Another Object 041"` myA i'venti'ol'is/ to provide evffec'tiveQlowlcst' Ineans for detecting t ep'rsenceV of a g'ourfdlona direct Current transmis?- siOn line While the' transi'iSsn/lne is energized' and which means may be conveniently operated by unskilled personnel.

yIn carrying out myin'vention in one embodiment thereof, a voltage divider'isA connected across an energizeddirect current" transmission' line. A cathode-follower circuit" and a capacitive remembering circuit cooperate to compensate the potential impressed on the voltage dividei`|` by' the transmission line' and to` inasure the' resistance to ground through the" voltage divider;

g The features of my invention which I'believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization' and method of operation, together W'ith furtl'e'objects and adv vantages thereof, may best be understood-by referenceto the following description takenin conne'ction` with the accomg'aying' drawing, in-

which each of the four figures is a schematic diagram ofV a diierent ground detector circuit embodying my invention. n

Referring to the drawings, the ground detector circuit illustrated in Fig. l'employs a resistance l ing on the voltmeter Il.

bridge arrangement for determining the magnitudeoffthe-leaisage resistance between the transmission lines and- I4 are the ratio armsv` d; The resistors-'fl 3 and of the resi-stance bridge arrangement. Resistors 3 and i andupotentinmveter 8 comprise the unknown arm of the bridge. Potentiometers 9 and l2 comprise the balancing arm of the bridge. A battery |16 cf known voltage, isl applied to the circuit to enable theresistanceto ground toV be measured.

The direct current supply conductors l andi' represent a direct current transmission? line and have connected between them thegenerator 6, the battery 1, and variousl loads, such as the motor 5. The resistors 3 andrepresent the leakage resistance to ground from conductors l and 2, respectiveiy. Resistors 3 and" 4 Varenot physical circuit elements, but their eiect is present nevertheless. Generator 6Vy batt-ery Land motor 5 have small internal inipedance.comparedY with the potentiometer B. The potentiometers 8 and 9` are arranged with a cominon slider ann Il).A Potentiorneters 84 and are assigned values ofV resistance having thesaine ratio to one another as do the ratio resistors I4 and i3, respectivelyLso that it is not necessary to rebalance the bridge after slider I8 is moved. ,A n

When the transmission line` is in its norxnal operating condition, that is, high leakage resistance, the resistance ofthe unknown arrn of the bridge rhust be determined to serve as a ref'- ere'ncey level for satisfactory operation'. This is done by balancing the bridge as hereinafter ex piained. y v

The eiTect onA the bridge circuit ofthe potential impressed on potentiometer A8 by generator B and battery l is neutralized by adjusting slider i0 to a position on potentiometer 8 corresponding to ground potential. This is done' when switch I5 is in Contact with terminal ld'. The correct position for slider isis indicated' bya null read- Switch 5 is now turned to Contact terminal |511 thereby connecting the battery I6 between the resistance bridge and ground. Potentiometer vI2 is adjusted to obtain a nuil reading on voltmeter il. The setting on calibrated potentiometer l2 gives an indication of the total resistance of the' unknown arm of the bridge under normal operating conditions.

If it is suspected that thev transmission line is" Side'oi" thel transmis'sion` line isy gioundeizll` The position of slider I with respect to the conductors I and 2 gives a direct indication to the operator which conductor is grounded, for a null is obtained when slider I0 is adjacent the grounded conductor.

For some applications of the detector illustrated in Fig. 1, potentiometer B must be constructed to withstand voltages of the order of 1000 volts. Potentiometer 9 must be carefully adjusted to obtain a null on voltmeter I1 before battery I6 is switched into the circuit. Each of the following embodiments eliminates the need for potentiometers capable of withstanding voltages of this magnitude and for precise adjustments.

The embodiments of my invention illustrated in Figs. 2, 3 and 4 all involve a direct current transmission line and loading on the transmission line similar to that shown in Fig. l. Wherever, corresponding elements are employed in more than one embodiment, the same designating numerals are used throughout.

Each of the following embodiments of my invention used an ammeter calibrated to indicate the leakage resistance directly. In each case, it is necessary to obtain the leakage resistance for normal operation to serve as a reference for determining the severity of subsequent grounded conditions.

The embodiment illustrated in Fig. 2 replaces the potentiometers 8 and 9 in Fig. 1 with a voltage divider I8 and a selector switch I9. The magnitudes of the series resistors ISa, |817, Ic, |841 and IBe are chosen so that the resistance between each of the contacts of switch I9 and the terminals of generator 6 is constant.

In the circuit illustrated in Fig. 2, there is a terminal on switch I9 having a potential with respect to ground within a predetermined range, such as 100 volts. When the triple-pole-doublethrow switch 20 is in the position to the left, a capacitive, or remembering circuit, such as the capacitor 2|, is connected between the voltage divider circuit and ground. The operator simply manipulates switch I9 to the terminal having 100 volts or less potential between the contact and ground. When one conductor of the transmission line is grounded, switch I9 must be moved to a terminal adjacent the grounded conductor to obtain a voltage of 100 volts or less. The voltmeter 22 indicates the Voltage between switch I9 and ground, and capacitor 2| is charged to this voltage.

The amplifier 23 is loaded in its cathode circuit. This arrangement is well known in the art as a cathode-follower circuit. The salient feature of the cathode-follower circuit is that it ca have substantially unity gain.

A source of direct potential, such as that supplied by the two power packs shown in Fig. 2, supplies the potentials required for the operation of the ground detector circuit. The output of rectifier 21 is of some value such as 400 volts above ground potential. Bleeder resistor 29 is connected between the output of rectier 21 and ground potential. The resistor 28 is connected between the cathode of amplifier 23 and the output lead of rectifier 21. The output of rectier 26 is of some Value such as 300 volts and is serially connected with the output of rectifier 21 so that the output lead of rectifier 26 is approximately '100 volts above ground potential.

cathodes of rectiers 28 and 21.

The` bleeder resistor 30 is connected between the.. The cathode` of rectier 26 is connected to the plate of amplier 23.

Terminal 20j of switch 20 is connected to resistor 30 at a point corresponding to some voltage, such as 500 Volts, above ground potential. The condensers 3| and 32 connected across the outputs of rectifiers 26 and 21 are merely filter condensers. The control electrode of amplifier 23 is connected to terminal 20e. An ammeter 33 having its scale calibrated in ohms is connected between terminal 20d and the cathode of amplifier 23.

When capacitor 2| is charged to the voltage between switch I9 and ground, switch 20 is thrown to its right-hand position thereby connecting switch I9 to terminal 20dl and connecting capacitor 2| between terminals 20e and 20]. The voltage on the control electrode of amplifier 23 now is equal to 500 Volts plus the voltage on switch I9 as remembered by capacitor 2|. The rapid increase in the grid voltage of amplifier 23 causes a sharp increase in the tube current. The increasing current raises the potential drop in resistors 28 and 29 thereby raising the potential of the cathode with respect to ground to the potential of the grid. The cathode potential stabilizes at this value. When the Voltage of the cathode is equal to 500 Volts plus the remembered voltage of switch I9 and is connected through ammeter 33 in opposition with the actual voltage on switch I9, a net voltage of 500 volts is impressed between ground and switch I9.

Ammeter 33 measures the current produced by the 500 volts through switch |9, resistor |817, the two paths to conductors I and 2 provided by voltage divider I8, and through any leakage resistance to ground. The resistance from switch I9 to the terminals of generator 6 is constant, and the total circuit resistance is equal to this constant plus the leakage resistance since the internal resistance of generator 6, battery 1, and motor 5 is small compared to voltage divider I8. By proper calibration, the ammeter can be made to read the leakage resistance directly. This resistance is then compared with the known leakage resistance for normal operation. The major advantage of the circuit of Fig. 2 is that the operator need make no precise adjustments.

In Fig. 2, a point on voltage divider I8 was selected Which was at a potential close to ground potential compared to the transmission line conductors. In Fig. 3 is shown an arrangement which produces a local voltage to neutralize whatever potential may appear at a fixed point on a voltage divider between conductors I and 2. This point is chosen to be substantially at ground potential under normal operating conditions. Voltage divider I8 is replaced in Fig. 3 by the resistors 34 and 35. The capacitive remembering circuit is still the capacitor 2| connected between the terminal 36a of the switch 3S and ground. Amplifier 23 is still connected in a cathod-follower circuit. In this case, the source of direct potential furnishing anode voltage is the battery 31.

A variable and reversible source of direct potential, such as apower pack, is used to raise the potential of the cathode-follower circuit to a level corresponding to the potential of switch 36. The variable ratio transformer 40 is connected to a source of alternating voltage and has its output connected to the primary windings of transformer 2.5. The output of transformer 25 is subjected to full-Wave rectification and connected acrossreversing switch 38.

The junction of resistors. 34 and 35 may be above or below ground potential, depending upon the relative magnitudes of resistorsA 3 andy '4. Therefore, the voltage'of the junction of resistor 28` and battery' 31 might be required to be either positive or negative'with respect'to ground, and itsfpolarity is changed-*by means of reversing switch 38.

While capacitor 2| is connected to' switch 36, the' voltage on the control electrode of ampli'- fieri 23'is equal to the' potential of switch 36 with respect to ground.- The cathode-'follower adjnstsfitsz cathode rpotential to its grid potential. After capacitor 2| is chargedto the potential ofs'witch 36, switch 35 is manipulated to contact terminal 36h. Now the potential of switch'36 as remembered by capacitor 2| is transmitted through the cathode-follower circuit and connected in opposition to the actual potential on switch. `36 through ammeter 33 and battery 4|'. The net potential on switch 36 is now equal to the known voltage of battery 4|. Thev reading obtained on ammeter 33 indicates the total-re'- sistance of resistors 34 and 35 in parallel, and in series with leakage resistors 3l and` 4in parall'el.` Since the resistance of resistors 34 and 35--in parallel is constant, ammeter33` can be calibrated to read directly the resistance of 3and-4 in parallel. This, of course, is the leakage resistance.

The ground: detector arrangement rillustrated in? Fig. 4 is substantially that shownin Fig. y3 withf the addition of motor driven means for automatically performing the manual operations described for' Fig. 3. The control motor 43drives a cam 43a which operates the switches r44v and 45' to simultaneously closer the contacts 46 and 41 and open? the contacts 48 andA 49 for a predetermined time interval, such 'as 58-rseconds out ofv each minute. Switchy 44 simply replaces switch 36 inFig. 3. o

A variable, reversible source of direct potential such asv the twin"` power pack shownfin Fig. 4 isvconnected' between the'c'athode-'fo'llower circuit and ground. The primary-ofeach ofA the transformers 53 and 54 is connected between one side' of variable-ratio transformer' 39' and the slider 39a on transformer 39. Each' of the anodes of rectier 55` is connected to `a diierent terminal f the secondary winding of transformer 53,y andv each' of the anodes' of .r'ecti'er 56' is connected to aA different terminal .l of the secondary winding of: transformer 54'.` Each of theca-thodes of rectiers 55 andi 56 isconnected tor adiiferentl terminal of the capacitor 51; The' y resistor" 5-8L is conneetedf'inL parallel relation with capacitor 5'1. The center points of resistor 58y y and the secondary windingsof transformers" 5'3 and 54" are connected together; MotorsV 43' and" '52fare1 energized' through the .alternating supply con'cluctors- 59- and 6.0'.-j

The: high-range relay, 552. and; theflow-range' relay 5| replace ammeter 42. andare'connected in series 1in; the anodey circuit.` of amplieri 23.

"Each relayy has a holding'coil mechanism cans-f in'g: it.r to drop out' at aflower currentv level than the level at which it picks up: IThe current level.Y at which relay. 5| lpicks up-.rissomewhat lower -than the:h current level. at whi'clif relai/i550 dropsv out...

. To: intimate'. intl-.conferendo drin-.laye su: and;

contacts 55h and 5|b; Motor 52 is energized milliamps and drops out at 6 milliamps. Relay 5| picks up at 4 millianips and drops out at 1.2 milliamps. When the current is between 4 milliamps and 10 milliamps, only relay 5| ypicks up. Relay 50 is also picked up when .the tube current gets above 10 milliamps. When the current decreases 170.6y milliamps, relay 5B drops out, and when the current decreases to 1.2 milliainps, relay V5| drops out.

The motor 52 is a reversible motor operating at a speed such as 4 revolutions per minute. Motor 43 operates at some speed such as 1 revolution per minute and can beenergized through contacts 41, or through contacts 49 and the contacts of r'elays'SO-and 5|. Reiays'50' and 5| operate contacts 50o and 50o, and 5ta and 5|b, respectively, to control motor 43 and motor 52.

In operation, switches 44 and 45 close the contactsy 48 and 49, respectively. Condenser 2| is chargedk to the potential ofthe point between resistor 34 and 35. This same potential is also ap'- plied to the control electrode of amplier 23.

Consider, rst, they condition in which amplifier 23 is biased substantially positive. When contacts 48 and 4Q are closed, the potential withY re-A spect to ground of the control electrode of ampli'- er 23 becomes substantially greater than the cathode potential with respect to ground.. A current of greater than 10 milliampsflow's in the anode circuit and relaysJ 5D and 5| pickup closing through its terminals 52o and 52`c and rotates in a clockwise direction changing the position of slider 39a on transformer 39, thereby increasing the potential across capacitor 51 and raising the potential of the cathode of amplier 23 with re'- spect to ground. As the cathode potential approaches the control electrode potential, the anode'current decreases to the 4 to 6 milliamp range. Relay 50' drops out and motor 43 is connected across the alternatingsupp'ly conductors 58' and 59"through contacts 55a and 5 lb.

When the cani 43a closes contacts 46 and 41 oncernore', the potential of the point between resistors 34 and 35 is .relnembered by capacitor 2| and'` applied to the'cont'rol electrode. The cathode-follower applies the remembered voltagelin series with battery 4| and in opposition to the voltage on the junction of resistors 34 and 35 thereby enablingammeter 33 to indicate theresis'tanceo-f the circuit,

Iffthe control electrode and the cathode" voltv agestof.amplifier` 23' are substantially the same whencontacts 1:8t are cio'sed, 4 to 6 milliampsnow iri the 'anode circuit. The cathode-follower' circuitladju'sts' itselfto mali-e' the cathode' and-control electrode' voltages" equal. n pckedluli Motor '4'3`co'nthde`s-t0`0prate through contacts 50a and'` 5F52 y C'iis'idernow the condition inewhichamplifl'er cuit;A Neither relay is picked up. Motor 52 is`vl onlyl relay' 5| rs' Contact eiectreciapotennaltnie tubecariie.' 'if creases to the 4 to 6 milliamp range. Relay 5| picks up, motor 52 is deenergized, and motor 43 is energized once more. When motor 43 is energized, the circuit continues to operate as hereinbefore described.

While my invention has been described by reference to particular embodiments thereof, it will be understood that this is by way of illustration of the principles involved and that those skilled in the art may make many modications in the arrangement and mode of operation. Therefore, I contemplate by the appended claims to cover any such modications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a direct current power transmission system having a pair of energized direct current supply conductors and having a leakage resistance between one of said conductors and ground, a circuit for detecting the presence of grounds on said energized direct current supply conductors, said ground detector circuit including said leakage resistance and comprising a resistive circuit connected across said supply conductors, a pair of resistances connected between said resistive circuit and ground, a resistance indicating device connected between a variable point on said resistive circuit and the common terminal of said resistances, and means for selectively connecting a unidirectional potential of fixed value across said pair of resistances to facilitate adjusting said variable point to measure the leakage resistance.

2. In a direct current power transmission system having a pair of energized direct current supply conductors having a leakage resistance to ground, a circuit for detecting the presence of grounds on said pair of energized direct current supply conductors, said ground detector circuit including said leakage resistance and comprising a rst potentiometer connected across said supply conductors, a source of direct potential, a second potentiometer having the end terminals thereof connected together, a calibrated variable resistor having a iirst terminal connected to said end terminals, a switching device for interposing said source of direct potential serially between said variable -resistor and ground, two ratio resistors serially connected between said rst terminal and ground, said rst and said second potentiometers having a common adjustable contact and the ratio between the magnitudes of the efective resistances of said rst and second potentiometers being substantially equal to the -corresponding ratio for said ratio resistors, and a resistance indicating device including said second potentiometer, said calibrated resistor, and an electric meter device responsive to voltages and connected between said common adjustable contact and the common terminal of said ratio resistors for indieating voltage difference therebetween.

3. In a direct current power transmission system having a pair of energized direct current supply conductors having a leakage resistance to ground, a circuit for detecting the presence of grounds on said pair of energized direct currentsupply conductors, said ground detector circuit comprising said leakage resistance, a resistive voltage divider connected across said supply conductors, said voltage divider having taps at discrete voltage levels thereon, a selector switch having a selector member and having contacts corresponding to said taps, a plurality of resistors,

a diierent one of said resistors connected between each of said contacts and the corresponding tap on said voltage divider, an electron discharge device having an anode, a cathode, and a control electrode, a source of direct potential connected between said anode and ground and having a terminal thereon for obtaining voltage at a predetermined level for measuring said leakage resistance, a resistor connected between said cathode and ground, a voltmeter, a capacitor, a switch having contacts for selectively connecting said capacitor between said selector member and ground and between said terminal and said control electrode, said last-mentioned switch also having contacts for connecting said voltmeter in parallel relationship with said capacitor when said capacitor is connected between said selector arm and ground, a resistance indicating device, and contacts on said last-mentioned switch for connecting said resistance indicating device between said cathode and said selector member when said capacitor is connected between said control electrode and said terminal.

4. In a direct current power transmission systern having a pair of energized direct current supply conductors and having a leakage resi-stance between each conductor and ground, a circuit for detecting the presence of grounds on said pair of energized direct current supply conductors comprising a resistive voltage divider connected across said supply conductors and having a tap at a determinable point thereon, an electron discharge device having an anode, a cathode, and a control electrode, a resistor connected to said cathode, a capacitor connected between said control electrode and ground, a switch having contacts for connecting said voltage divider tap between said capacitor and said control electrode, a resistance indicating device, a source of direct potential serially connected with said resistance indieating device, said switch also having contacts for connecting said Voltage divider tap to said cathode through said resistance indicating device and said source of direct potential, a reversing switch, and a variable source of direct potential connected through said reversing switch between ground and said cathode resistor.

5. In a direct current power transmission system having a pair of energized direct current supply conductors and having a leakage resistance between each conductor and ground, a circuit for detecting the presence of grounds on said pair of energized direct current supply conductors and comprising a resistive circuit connected across said supply conductors, an electron discharge device having an anode, a cathode, and a control electrode, a series circuit connecting said anode to said cathode, a high-range relay serially connected in said anode circuit responsive to a rst predetermined value of current to pick up and responsive to a second predetermined value of current to drop out, a low-range relay serially connected in said anode circuit responsive to a third predetermined value of current to pick upand responsive to a fourth predetermined value of current to drop out, each of said predetermined values of current being of smaller magnitude than the -preceding predetermined value of current, a cathode resistor serially connected in said anode circuit and having one end connected to said cathode, a capacitor connected between the other end of said cathode resistor and ground, a circuit including a capacitor connecting said control electrode to ground, a variable and reversible source of direct potential, a reversible electric motor, a

pair of alternating current supply conductors, a. circuit for-energizing said reversible motor, contacts in series in said reversible motor circuit and operated by said relays for controlling said reversible motor, means driven by said reversible motor varying and reversing said variable and reversible 'source of `direct potential, a control motor, a first circuit for energizing said control motor, contacts in series in said rst control motor circuit and operated by said relays for controlling the operation of said control motor, a second -control motor circuit for connecting said control motor across said alternating supply conductors, cams mounted for rotation by said control motor. switching devices operated by said cams and having contacts for simultaneously connecting a predetermined point in said resistive circuit -to said control electrode circuit between lsaid control electrode and said capacitor and connecting said control motor in said first control motor circuit, a

resistance indicating device, a second source of direct potential, said switching devices also having contacts for simultaneously connecting said control motor in said second control motor circuit and connecting said predetermined point of said resistive circuit to said cathode through a series circuit consisting of said second source of direct potential and said resistance indicating device.

THEODORE A. RICH.

REFERENCES CITED UNITED STATES PATENTS Name Date Corderman Dec. 3, 1935 Number 

